DNN TextEditor width not follow the HTML Input properties in Control Panel

Changing the Width in HTML INPUT Features Properties for a forum for the DNNTextEditor I obtain resized the AF objects (input fields, attachments and pools sections...). But the DNN text edito for the body not follow this setting. I've always a text box
about 650px width with a horizontal scrollbar.

The height setitng, instead, is correctly used. How may I fix the textbox widht?